1. Technical Field
The present invention relates to a reduced-pressure drying apparatus that is used when work to which some liquid is applied is dried under reduced pressure so as to form a film on the surface of the work.
2. Related Art
A reduced-pressure drying apparatus in which a solvent component in a liquid is vaporized and dried out is used for forming a film on a wafer-like substrate such as a semiconductor substrate by applying the liquid containing a film formation material. JP-A-2002-313709 is an example of related art. The example proposed the reduced-pressure drying apparatus in which a substrate to which photoresist is applied is placed in a reduced-pressure chamber. A rectifying plate is provided so as to oppose the substrate and a venting hole is provided on the peripheral of the rectifying plate.
The above-mentioned reduced-pressure drying apparatus exhausts from the upper part of the chamber and this forms a unidirectional air flow that starts from around the peripheral of the wafer-like substrate and streams through the venting hole of the rectifying plate to an exhaust outlet. Accordingly, the velocity of the air flow running between the rectifying plate and the substrate becomes uniform in the substrate plane. Therefore, the thickness of the film is made even in the substrate plane and it is possible to form the film with a uniform thickness on the substrate.
As described above, many electronic devices including semiconductors have a manufacturing process in which a liquid containing a functional material is applied to work such as a wafer in order to form a film made of the functional liquid on the surface of the work.
However, in a drying process in which the liquid is dried to form the film, it is very difficult to dry the liquid so as to form the film having a completely uniform thickness throughout the film when it is under the formation on the surface of the work or after the formation, and even with the above-described reduced-pressure drying apparatus. This is because many kinds of liquid can be used and a saturated vapor pressure and rheological properties (viscosity, elasticity, plasticity, thixotropy and the like) vary according to each kind of the liquid. In addition, behaviors of the liquid such as an evaporation rate during the drying process also vary according to volumes and a surface area ratio of a solute and a solvent contained in the liquid.
Even when the above-described hitherto known reduced-pressure drying apparatus has the rectifying plate in order to control the air flow of a solvent which evaporated from the liquid under a reduced-pressure to have a uniform velocity in a constant direction, a movement (convection flow) of the liquid is generated in the drying process and the uniformity of the film thickness is deteriorated by surface tension. Furthermore, vapor concentration (or pressure) distribution differs from a center part to a peripheral part, resulting in the film thickness in-plane distribution caused by a difference in drying rate. Moreover, if the drying apparatus has to be optimally redesigned according to kinds of the liquid material or a configuration of the work to which the liquid is applied, the versatility of the apparatus cannot be secured.